The wheel suspension is the connecting link between a wheel and the chassis of a vehicle. The connection is formed by axles or comparable structures, the steering management is implemented by so called guide rods. Generally, these are struts, which are attached to the chassis and fix the wheel suspension in position. One distinguishes between transverse control arms, semi-trailing arms and trailing arms. Today, transverse control arms, which are positioned approximately in the direction of travel, are mostly used in modern passenger cars, in order to fix the wheel in position horizontally and to allow vertical movement. While driving in the direction of travel (straight ahead), the wheel should rotate about a fixed axis of rotation, which is mainly determined by the transverse control arm and the wheel bearing.
Wheel bearings and transverse control arms are parts subject to wear, which may wear out or may also be damaged. Generally, damage to or wear of a wheel bearing or transverse control arm may be recognized visually from the outside, since they are attached to the inner side of the wheel rim. In curves, in particular, which are driven through rapidly, defective or worn wheel bearings generate a background noise, which is a function of the speed. Worn transverse control arms result in uneven straight-ahead travel, which is also referred to as floating of the vehicle. Due to the reduced stability of the wheels caused by the untrue motion of the wheels, the rolling resistance also increases, thereby increasing the fuel consumption.
Apart from the regular replacement of the part subject to wear, that is, the wheel bearing, defective wheel suspensions, whether faulty wheel bearings or transverse control arms, have been detected visually up to this point. In addition to this, an experienced mechanic may detect a defect due to shaking of the lifted-off wheel. Outside of the inspection intervals, this occurs mostly when, due to the handling at higher speeds, a corresponding indication is present. However, inexperienced drivers may fail to notice such an indication, which, during an inspection, would result in the diagnosis of a defect of the wheel suspension.